i8o INVERTEBRATE PALAEONTOLOGY 



its pentagonal columnals abound in rocks of Jurassic 

 age. The two most peculiar Inadunates are Uintacrinus 

 and Marsupites, both restricted to the Upper Cretaceous. 

 Unlike most free-swimming Crinoids, these types in- 

 creased, rather than reduced, the size of their calyces, 

 the former by incorporation of numerous small brachials 

 (a secondary " Camerate " quality), the latter by enlarge- 

 ment of the plates of the normal cycles. Both types 

 had exceedingly short careers, that of Uintacrinus 

 immediately preceding that of Marsupites. They are 

 used as zonal indices in the Upper Chalk. Flexibilia 

 were equally important in the Mesozoic. Apiocrinus 

 (the " pear-encrinite ") (PL xiii. fig. 2) is^ a well-known 

 Bathonian type. Specimens complete from root to 

 crown have been found in the Bradford Clay ; the dis- 

 coid columnals are abundant on slabs of Forest Marble. 

 BourgueticrimiSy a small allied genus, is universally 

 abundant in the Upper Chalk ; its varied shape has 

 some zonal significance. Rhizocrinus continues this series 

 in modern faunas. Free-swimming types of this order 

 predominate at the present day, and were well differenti- 

 ated in the Mesozoic. The small size and delicate 

 construction of " Feather-Stars " make them rare and 

 obscure in the fossil state. Millericrinus (PL i. fig. 3), 

 a type locally abundant in the Bathonian and Corallian, 

 though akin to Apiocrinus ', shows an early stage in 

 atrophy of the stem. Antedon (sens, lat.) is known from 

 the Lias, and may often be collected during search for 

 Chalk Microzoa. 



Holothurians of essentially modern aspect occur in 

 Solenhofen " Slate." Stelleroids are abundant through- 

 out the era, but entire specimens are rare. Ophioderma 

 produces a local "starfish-bed" in the Middle Lias. 

 Large marginals of Phanerozonate Asteroids are 

 abundant in the Oolites, and ubiquitous in the Chalk. 



